68 F/B rear seat carpet underlay ???

Thanks Tom, I took these seats apart about 2 years ago and put new seat covers on. The original paper board and carpet were in such bad shape that it was hard to tell what it looked like. I assumed it was some rigid type of thin fiberboard and that it's purpose was to provide a firm flat surface for the carpet to bond to .

Can you feel the grooves in the metal below the carpet on yours ?

I used 1/8 thick Masonite (fiber) board on my cuda. I didn't won't to feel the grooves in the metal... I wanted it flush looking. I didn't have any trouble with re installing the trim. I used the old piece of thick paper to trace the shape on the Masonite. Worked for me. Good luck!